package fastcgi

import (
	"bufio"
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"log"
	"mime"
	"net"
	"net/http"
	"net/http/httputil"
	"net/textproto"
	"strconv"
	"strings"
	"sync"
	"time"
)

const FCGI_LISTENSOCK_FILENO uint8 = 0
const FCGI_HEADER_LEN uint8 = 8
const VERSION_1 uint8 = 1
const FCGI_NULL_REQUEST_ID uint8 = 0
const FCGI_KEEP_CONN uint8 = 1
const doubleCRLF = "\r\n\r\n"

const (
	FCGI_BEGIN_REQUEST uint8 = iota + 1
	FCGI_ABORT_REQUEST
	FCGI_END_REQUEST
	FCGI_PARAMS
	FCGI_STDIN
	FCGI_STDOUT
	FCGI_STDERR
	FCGI_DATA
	FCGI_GET_VALUES
	FCGI_GET_VALUES_RESULT
	FCGI_UNKNOWN_TYPE
	FCGI_MAXTYPE = FCGI_UNKNOWN_TYPE
)

const (
	FCGI_RESPONDER uint8 = iota + 1
	FCGI_AUTHORIZER
	FCGI_FILTER
)

const (
	FCGI_REQUEST_COMPLETE uint8 = iota
	FCGI_CANT_MPX_CONN
	FCGI_OVERLOADED
	FCGI_UNKNOWN_ROLE
)

const (
	FCGI_MAX_CONNS  string = "MAX_CONNS"
	FCGI_MAX_REQS   string = "MAX_REQS"
	FCGI_MPXS_CONNS string = "MPXS_CONNS"
)

const (
	maxWrite = 65500 // 65530 may work, but for compatibility
	maxPad   = 255
)

type header struct {
	Version       uint8
	Type          uint8
	Id            uint16
	ContentLength uint16
	PaddingLength uint8
	Reserved      uint8
}

// for padding so we don't have to allocate all the time
// not synchronized because we don't care what the contents are
var pad [maxPad]byte

func (h *header) init(recType uint8, reqId uint16, contentLength int) {
	h.Version = 1
	h.Type = recType
	h.Id = reqId
	h.ContentLength = uint16(contentLength)
	h.PaddingLength = uint8(-contentLength & 7)
}

type record struct {
	h    header
	rbuf []byte
}

func (rec *record) read(r io.Reader) (buf []byte, err error) {
	if err = binary.Read(r, binary.BigEndian, &rec.h); err != nil {
		return
	}
	if rec.h.Version != 1 {
		err = errors.New("fcgi: invalid header version")
		return
	}
	if rec.h.Type == FCGI_END_REQUEST {
		err = io.EOF
		return
	}
	n := int(rec.h.ContentLength) + int(rec.h.PaddingLength)
	if len(rec.rbuf) < n {
		rec.rbuf = make([]byte, n)
	}
	if n, err = io.ReadFull(r, rec.rbuf[:n]); err != nil {
		return
	}
	buf = rec.rbuf[:int(rec.h.ContentLength)]

	return
}

type FCGIClient struct {
	mutex     sync.Mutex
	rwc io.ReadWriteCloser
	h   header
	buf bytes.Buffer
	keepAlive bool
	reqId     uint16

	FlushInterval time.Duration
}

// Connects to the fcgi responder at the specified network address.
// See func net.Dial for a description of the network and address parameters.
func Dial(network, address string) (fcgi *FCGIClient, err error) {
	var conn net.Conn

	conn, err = net.Dial(network, address)
	if err != nil {
		return
	}

	fcgi = &FCGIClient{
		rwc:       conn,
		keepAlive: false,
		reqId:     1,
	}

	return
}

// Connects to the fcgi responder at the specified network address with timeout
// See func net.DialTimeout for a description of the network, address and timeout parameters.
func DialTimeout(network, address string, timeout time.Duration) (fcgi *FCGIClient, err error) {

	var conn net.Conn

	conn, err = net.DialTimeout(network, address, timeout)
	if err != nil {
		return
	}

	fcgi = &FCGIClient{
		rwc:       conn,
		keepAlive: false,
		reqId:     1,
	}

	return
}

// Close fcgi connnection
func (that *FCGIClient) Close() {
	that.rwc.Close()
}

func (that *FCGIClient) writeRecord(recType uint8, content []byte) (err error) {
	that.mutex.Lock()
	defer that.mutex.Unlock()
	that.buf.Reset()
	that.h.init(recType, that.reqId, len(content))
	if err := binary.Write(&that.buf, binary.BigEndian, that.h); err != nil {
		return err
	}
	if _, err := that.buf.Write(content); err != nil {
		return err
	}
	if _, err := that.buf.Write(pad[:that.h.PaddingLength]); err != nil {
		return err
	}
	_, err = that.rwc.Write(that.buf.Bytes())
	return err
}

func (that *FCGIClient) writeBeginRequest(role uint16, flags uint8) error {
	b := [8]byte{byte(role >> 8), byte(role), flags}
	return that.writeRecord(FCGI_BEGIN_REQUEST, b[:])
}

func (that *FCGIClient) writeEndRequest(appStatus int, protocolStatus uint8) error {
	b := make([]byte, 8)
	binary.BigEndian.PutUint32(b, uint32(appStatus))
	b[4] = protocolStatus
	return that.writeRecord(FCGI_END_REQUEST, b)
}

func (that *FCGIClient) writePairs(recType uint8, pairs map[string]string) error {
	w := newWriter(that, recType)
	b := make([]byte, 8)
	nn := 0
	for k, v := range pairs {
		m := 8 + len(k) + len(v)
		if m > maxWrite {
			// param data size exceed 65535 bytes"
			vl := maxWrite - 8 - len(k)
			v = v[:vl]
		}
		n := encodeSize(b, uint32(len(k)))
		n += encodeSize(b[n:], uint32(len(v)))
		m = n + len(k) + len(v)
		if (nn + m) > maxWrite {
			w.Flush()
			nn = 0
		}
		nn += m
		if _, err := w.Write(b[:n]); err != nil {
			return err
		}
		if _, err := w.WriteString(k); err != nil {
			return err
		}
		if _, err := w.WriteString(v); err != nil {
			return err
		}
	}
	w.Close()
	return nil
}

func readSize(s []byte) (uint32, int) {
	if len(s) == 0 {
		return 0, 0
	}
	size, n := uint32(s[0]), 1
	if size&(1<<7) != 0 {
		if len(s) < 4 {
			return 0, 0
		}
		n = 4
		size = binary.BigEndian.Uint32(s)
		size &^= 1 << 31
	}
	return size, n
}

func readString(s []byte, size uint32) string {
	if size > uint32(len(s)) {
		return ""
	}
	return string(s[:size])
}

func encodeSize(b []byte, size uint32) int {
	if size > 127 {
		size |= 1 << 31
		binary.BigEndian.PutUint32(b, size)
		return 4
	}
	b[0] = byte(size)
	return 1
}

// bufWriter encapsulates bufio.Writer but also closes the underlying stream when
// Closed.
type bufWriter struct {
	closer io.Closer
	*bufio.Writer
}

func (w *bufWriter) Close() error {
	if err := w.Writer.Flush(); err != nil {
		w.closer.Close()
		return err
	}
	return w.closer.Close()
}

func newWriter(c *FCGIClient, recType uint8) *bufWriter {
	s := &streamWriter{c: c, recType: recType}
	w := bufio.NewWriterSize(s, maxWrite)
	return &bufWriter{s, w}
}

// streamWriter abstracts out the separation of a stream into discrete records.
// It only writes maxWrite bytes at a time.
type streamWriter struct {
	c       *FCGIClient
	recType uint8
}

func (w *streamWriter) Write(p []byte) (int, error) {
	nn := 0
	for len(p) > 0 {
		n := len(p)
		if n > maxWrite {
			n = maxWrite
		}
		if err := w.c.writeRecord(w.recType, p[:n]); err != nil {
			return nn, err
		}
		nn += n
		p = p[n:]
	}
	return nn, nil
}

func (w *streamWriter) Close() error {
	// send empty record to close the stream
	return w.c.writeRecord(w.recType, nil)
}

type streamReader struct {
	c   *FCGIClient
	buf []byte
}

func (w *streamReader) Read(p []byte) (n int, err error) {

	if len(p) > 0 {
		if len(w.buf) == 0 {
			rec := &record{}
			w.buf, err = rec.read(w.c.rwc)
			if err != nil {
				return
			}
		}

		n = len(p)
		if n > len(w.buf) {
			n = len(w.buf)
		}
		copy(p, w.buf[:n])
		w.buf = w.buf[n:]
	}

	return
}

// Do made the request and returns a io.Reader that translates the data read
// from fcgi responder out of fcgi packet before returning it.
func (that *FCGIClient) Do(p map[string]string, req io.Reader) (r io.Reader, err error) {
	err = that.writeBeginRequest(uint16(FCGI_RESPONDER), 0)
	if err != nil {
		return
	}

	err = that.writePairs(FCGI_PARAMS, p)
	if err != nil {
		return
	}

	body := newWriter(that, FCGI_STDIN)
	if req != nil {
		io.Copy(body, req)
	}
	body.Close()

	r = &streamReader{c: that}
	return
}

type badStringError struct {
	what string
	str  string
}

func (e *badStringError) Error() string { return fmt.Sprintf("%s %q", e.what, e.str) }

// Request returns an HTTP Response with Header and Body
// from fcgi responder
func (that *FCGIClient) Request(p map[string]string, req *http.Request) (resp *http.Response, err error) {
	p["REQUEST_METHOD"] = req.Method

	if req.Method == "GET" {
		p["CONTENT_LENGTH"] = "0"
		//return that.Request(param, nil)
	} else if req.Method == "POST" {
		p["CONTENT_LENGTH"] = req.Header.Get("Content-Length")
		if len(req.Header.Get("Content-Type")) > 0 {
			p["CONTENT_TYPE"] = req.Header.Get("Content-Type")
		} else {
			p["CONTENT_TYPE"] = "application/x-www-form-urlencoded"
		}
	}
	r, err := that.Do(p, req.Body)
	if err != nil {
		return
	}
	rb := bufio.NewReader(r)
	tp := textproto.NewReader(rb)
	resp = new(http.Response)
	// Parse the first line of the response.
	line, err := tp.ReadLine()

	if err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return nil, err
	}
	var statusCode string
	if len(line) > 5 && line[:5] == "Status" {
		if i := strings.IndexByte(line, ' '); i == -1 {
			err = &badStringError{"malformed HTTP response", line}
		} else {
			resp.Proto = line[:i]
			resp.Status = strings.TrimLeft(line[i+1:], " ")
		}
		statusCode = resp.Status
		if i := strings.IndexByte(resp.Status, ' '); i != -1 {
			statusCode = resp.Status[:i]
		}
	} else {
		resp.Status = "200 OK"
		statusCode = "200"
	}

	if len(statusCode) != 3 {
		err = &badStringError{"malformed HTTP status code", statusCode}
	}
	resp.StatusCode, err = strconv.Atoi(statusCode)
	if err != nil || resp.StatusCode < 0 {
		err = &badStringError{"malformed HTTP status code", statusCode}
	}
	var ok bool
	if resp.ProtoMajor, resp.ProtoMinor, ok = http.ParseHTTPVersion(resp.Proto); !ok {
		err = &badStringError{"malformed HTTP version", resp.Proto}
	}
	// Parse the response headers.
	mimeHeader, err := tp.ReadMIMEHeader()

	if err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return nil, err
	}
	resp.Header = http.Header(mimeHeader)
	// TODO: fixTransferEncoding ?
	resp.TransferEncoding = resp.Header["Transfer-Encoding"]
	//resp.ContentLength, _ = strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64)

	if chunked(resp.TransferEncoding) {
		resp.Body = io.NopCloser(httputil.NewChunkedReader(rb))
	} else {
		//fmt.Println("fast cgi nopcloser")
		//resp.Body = io.NopCloser(rb)

		body, _ := io.ReadAll(rb)
		//fmt.Println("fastcgi body:", string(body), "===========")
		resp.Body = io.NopCloser(bytes.NewReader(body))

	}
	return
}

// Get issues a GET request to the fcgi responder.
func (that *FCGIClient) Get(p map[string]string) (resp *http.Response, err error) {

	p["REQUEST_METHOD"] = "GET"
	p["CONTENT_LENGTH"] = "0"

	return that.Request(p, nil)
}

// Get issues a Post request to the fcgi responder. with request body
// in the format that bodyType specified
/*func (that *FCGIClient) Post(p map[string]string, bodyType string, body io.Reader, l int) (resp *http.Response, err error) {

	if len(p["REQUEST_METHOD"]) == 0 || p["REQUEST_METHOD"] == "GET" {
		p["REQUEST_METHOD"] = "POST"
	}
	p["CONTENT_LENGTH"] = strconv.Itoa(l)
	if len(bodyType) > 0 {
		p["CONTENT_TYPE"] = bodyType
	} else {
		p["CONTENT_TYPE"] = "application/x-www-form-urlencoded"
	}

	return that.Request(p, body)
}*/

// PostForm issues a POST to the fcgi responder, with form
// as a string key to a list values (url.Values)
/*func (that *FCGIClient) PostForm(p map[string]string, data url.Values) (resp *http.Response, err error) {
	body := bytes.NewReader([]byte(data.Encode()))
	return that.Post(p, "application/x-www-form-urlencoded", body, body.Len())
}*/

// PostFile issues a POST to the fcgi responder in multipart(RFC 2046) standard,
// with form as a string key to a list values (url.Values),
// and/or with file as a string key to a list file path.
/*func (that *FCGIClient) PostFile(p map[string]string, data url.Values, file map[string]string) (resp *http.Response, err error) {
	buf := &bytes.Buffer{}
	writer := multipart.NewWriter(buf)
	bodyType := writer.FormDataContentType()

	for key, val := range data {
		for _, v0 := range val {
			err = writer.WriteField(key, v0)
			if err != nil {
				return
			}
		}
	}

	for key, val := range file {
		fd, e := os.Open(val)
		if e != nil {
			return nil, e
		}
		defer fd.Close()

		part, e := writer.CreateFormFile(key, filepath.Base(val))
		if e != nil {
			return nil, e
		}
		_, err = io.Copy(part, fd)
	}

	err = writer.Close()
	if err != nil {
		return
	}

	return that.Post(p, bodyType, buf, buf.Len())
}*/

// Checks whether chunked is part of the encodings stack
func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }

func copyHeader(dst, src http.Header) {
	for k, vv := range src {
		for _, v := range vv {
			dst.Add(k, v)
		}
	}
}

// switchProtocolCopier exists so goroutines proxying data back and
// forth have nice names in stacks.
type switchProtocolCopier struct {
	user, backend io.ReadWriter
}

func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
	_, err := io.Copy(c.user, c.backend)
	errc <- err
}

func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
	_, err := io.Copy(c.backend, c.user)
	errc <- err
}

// removeHopByHopHeaders removes hop-by-hop headers.
func removeHopByHopHeaders(h http.Header) {
	// RFC 7230, section 6.1: Remove headers listed in the "Connection" header.
	for _, f := range h["Connection"] {
		for _, sf := range strings.Split(f, ",") {
			if sf = textproto.TrimString(sf); sf != "" {
				h.Del(sf)
			}
		}
	}
	// RFC 2616, section 13.5.1: Remove a set of known hop-by-hop headers.
	// This behavior is superseded by the RFC 7230 Connection header, but
	// preserve it for backwards compatibility.
	for _, f := range hopHeaders {
		h.Del(f)
	}
}

// Hop-by-hop headers. These are removed when sent to the backend.
// As of RFC 7230, hop-by-hop headers are required to appear in the
// Connection header field. These are the headers defined by the
// obsoleted RFC 2616 (section 13.5.1) and are used for backward
// compatibility.
var hopHeaders = []string{
	"Connection",
	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
	"Keep-Alive",
	"Proxy-Authenticate",
	"Proxy-Authorization",
	"Te",      // canonicalized version of "TE"
	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
	"Transfer-Encoding",
	"Upgrade",
}

func (that *FCGIClient) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
	if flushInterval != 0 {
		if wf, ok := dst.(writeFlusher); ok {
			mlw := &maxLatencyWriter{
				dst:     wf,
				latency: flushInterval,
			}
			defer mlw.stop()

			// set up initial timer so headers get flushed even if body writes are delayed
			mlw.flushPending = true
			mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)

			dst = mlw
		}
	}

	var buf []byte
	_, err := that.copyBuffer(dst, src, buf)
	return err
}

type writeFlusher interface {
	io.Writer
	http.Flusher
}
type maxLatencyWriter struct {
	dst     writeFlusher
	latency time.Duration // non-zero; negative means to flush immediately

	mu           sync.Mutex // protects t, flushPending, and dst.Flush
	t            *time.Timer
	flushPending bool
}

func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	n, err = m.dst.Write(p)
	if m.latency < 0 {
		m.dst.Flush()
		return
	}
	if m.flushPending {
		return
	}
	if m.t == nil {
		m.t = time.AfterFunc(m.latency, m.delayedFlush)
	} else {
		m.t.Reset(m.latency)
	}
	m.flushPending = true
	return
}

func (m *maxLatencyWriter) delayedFlush() {
	m.mu.Lock()
	defer m.mu.Unlock()
	if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
		return
	}
	m.dst.Flush()
	m.flushPending = false
}

func (m *maxLatencyWriter) stop() {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.flushPending = false
	if m.t != nil {
		m.t.Stop()
	}
}

func (that *FCGIClient) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
	if len(buf) == 0 {
		buf = make([]byte, 32*1024)
	}
	var written int64
	for {
		nr, rerr := src.Read(buf)
		if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
			log.Fatal("httputil: ReverseProxy read error during body copy: %v", rerr)
		}
		if nr > 0 {
			nw, werr := dst.Write(buf[:nr])
			if nw > 0 {
				written += int64(nw)
			}
			if werr != nil {
				return written, werr
			}
			if nr != nw {
				return written, io.ErrShortWrite
			}
		}
		if rerr != nil {
			if rerr == io.EOF {
				rerr = nil
			}
			return written, rerr
		}
	}
}

// flushInterval returns the p.FlushInterval value, conditionally
// overriding its value for a specific request/response.
func (that *FCGIClient) flushInterval(res *http.Response) time.Duration {
	resCT := res.Header.Get("Content-Type")

	// For Server-Sent Events responses, flush immediately.
	// The MIME type is defined in https://www.w3.org/TR/eventsource/#text-event-stream
	if baseCT, _, _ := mime.ParseMediaType(resCT); baseCT == "text/event-stream" {
		return -1 // negative means immediately
	}

	// We might have the case of streaming for which Content-Length might be unset.
	if res.ContentLength == -1 {
		return -1
	}

	return that.FlushInterval
}

// shouldPanicOnCopyError reports whether the reverse proxy should
// panic with http.ErrAbortHandler. This is the right thing to do by
// default, but Go 1.10 and earlier did not, so existing unit tests
// weren't expecting panics. Only panic in our own tests, or when
// running under the HTTP server.
func shouldPanicOnCopyError(req *http.Request) bool {
	if req.Context().Value(http.ServerContextKey) != nil {
		// We seem to be running under an HTTP server, so
		// it'll recover the panic.
		return true
	}
	// Otherwise act like Go 1.10 and earlier to not break
	// existing tests.
	return false
}
